We consider a \(K\) -tap doubly selective, narrowband radar channel model as \(h(t, \tau ) = \sum _{k=0}^{K-1} \alpha _k \delta (\tau - \tau _k) e^{j 2 \pi \nu _k t}\)  [1]}, [2]},
where the \( {k^{\rm {th} } } \)  target is characterized by a complex channel gain \(\alpha _k\) , a round-trip delay \( \tau _k = 2 R_k/c\)  and a Doppler shift \( \nu _k = 2  v_k / \lambda \) , with \(R_k\) , \( v_k \) , \(c\)  and \(\lambda \)  denoting the range, radial velocity, speed of propagation and carrier wavelength, respectively.
